The instruments used for testing are the same as those used for testing positioning accuracy. The general detection method is to measure at any three positions close to the midpoint and both ends of each coordinate stroke, each position is positioned with rapid movement, and the positioning is repeated 7 times under the same conditions, the value of the stop position is measured, and the maximum difference between the readings is obtained. . One-half of the largest difference in the three positions is attached with a positive and negative sign, as the repeated positioning accuracy of the coordinate, which is the most basic index reflecting the stability of the axis motion accuracy.
The positioning accuracy of linear motion is generally carried out under no-load conditions of the machine tool and the worktable.
According to the national standards and the regulations of the International Organization for Standardization (ISO standard), the detection of CNC machine tools should be based on laser measurement. In the absence of a laser interferometer, a standard scale can also be used for comparison measurements with an optical reading microscope for ordinary users. However, the accuracy of the measuring instrument must be 1 to 2 grades higher than the accuracy of the measurement. In order to reflect all the errors in multiple positioning, the ISO standard stipulates that each positioning point calculates the average value and dispersion difference according to the five measurement data, and the dispersion difference band of the positioning point is formed by the dispersion difference band.
The origin return accuracy is essentially the repeated positioning accuracy of a special point on the coordinate axis, so its detection method is completely the same as the repeated positioning accuracy.
The detection method of the reverse error is to move a distance in the forward or reverse direction in advance within the stroke of the measured coordinate axis and use this stop position as the reference, and then give a certain movement command value in the same direction to move it for a certain distance. Then move the same distance in the opposite direction, and measure the difference between the stop position and the reference position. Perform multiple measurements (usually 7 times) at three positions near the midpoint and both ends of the stroke, obtain the average value of each position, and take the maximum value of the obtained average value as the reverse error value.
The measurement method is to turn the worktable forward (or reversely) at an angle and stop, lock, and position it, take this position as a reference, and then quickly turn the worktable in the same direction, lock and position it every 30 degrees, and measure. The forward rotation and reverse rotation are each measured for one cycle, and the maximum value of the difference between the actual rotation angle of each positioning position and the theoretical value (command value) is the indexing error.
The measurement method is to repeat the positioning three times at any three positions within one week of the rotary table, and perform detection under the forward and reverse rotations respectively. The maximum indexing accuracy of the difference between all readings and the theoretical value of the corresponding position.
The measurement method is to perform a return-to-origin from 7 arbitrary positions, measure the stop position, and use the maximum difference read out as the return-to-origin accuracy. It should be pointed out that the detection of the existing positioning accuracy is measured under the condition of fast and positioning. For some CNC machine tools with a poor feed system, different positioning accuracy values will be obtained when positioning with different feed speeds.